Biology Fundamentals: Cell Structure to Genetics

Posted on Feb 12, 2026 in Biology

Module 1: Cells as the Basis of Life

Key Concepts

• Cell Theory: All organisms are made of cells; cells are the basic units of life; all cells arise from pre-existing cells.
• Prokaryotes vs. Eukaryotes:
  • Prokaryotes: No nucleus or membrane-bound organelles.
  • Eukaryotes: Complex, possess membrane-bound organelles.

Organelles & Functions

Transport Mechanisms

• Passive Transport: Diffusion, osmosis, facilitated diffusion (requires no ATP).
• Active Transport: Uses ATP via carrier proteins.
• Bulk Transport: Endo/exocytosis.

Enzymes

• Biological catalysts that lower activation energy.
• Influenced by temperature, pH, and substrate concentration.

Module 2: Organisation of Living Things

Hierarchy of Life

Cell → Tissue → Organ → System → Organism.

Transport Systems

• Plants:
  • Xylem: Transports water and minerals (unidirectional).
  • Phloem: Transports sugars via translocation (bidirectional).
• Animals:
  • Circulatory system transports gases, nutrients, and wastes.

Gas Exchange

• Plants: Stomata and guard cells regulate CO₂ and O₂ exchange.
• Animals: Alveoli or gills provide large surface area, thin, moist membranes.

Homeostasis

• Regulation of the internal environment through feedback mechanisms (e.g., temperature, water, glucose levels).

Module 3: Biological Diversity

Natural Selection Steps

1. Variation exists within a population.
2. Selection pressure acts on the population.
3. Favourable traits lead to increased survival and reproduction.
4. Allele frequencies change over generations.

Adaptations

• Structural: Physical features (e.g., beak shape).
• Physiological: Internal processes (e.g., salt excretion).
• Behavioural: Actions (e.g., migration).

Speciation

• Isolation leads to no gene flow, causing genetic divergence and potentially forming a new species.

Evidence for Evolution

• Fossils, comparative anatomy (homologous structures), embryology, and biochemistry (DNA hybridisation).

Module 4: Ecosystem Dynamics

Key Processes

• Energy Flow: Sun → producers → consumers → decomposers.
• Matter Cycles: Carbon, nitrogen, phosphorus, and water cycles.

Interactions

• Mutualism, commensalism, parasitism, predation, and competition.

Succession

• Primary: Occurs on new land (e.g., lava); progresses from pioneer species to a climax community.
• Secondary: Regrowth following a disturbance.

Human Impacts

• Habitat destruction, pollution, introduction of invasive species, and climate change.

Conservation Methods

• Restoration, captive breeding programs, seed banks, and establishment of national parks.

Module 5: Heredity

DNA Structure

• A double helix composed of nucleotides (sugar + phosphate + base).
• Base pairing rules: Adenine (A) pairs with Thymine (T); Guanine (G) pairs with Cytosine (C).

Cell Division

• Mitosis: Produces identical cells for growth and repair.
• Meiosis: Produces gametes, ensuring genetic variation.

Inheritance Principles

• Genotype determines Phenotype.
• Concepts include dominant, recessive, codominant, and incomplete dominance.
• Punnett squares predict expected genetic ratios.

DNA Replication

• It is semi-conservative: each new DNA molecule contains one original strand and one newly synthesized strand.

Module 6: Genetic Change

Mutations

• Types: Gene mutations (point or frameshift) or chromosomal mutations (deletion, duplication, translocation).
• Caused by mutagens such as radiation, chemicals, or viruses.

Biotechnology Techniques

• Selective breeding.
• Recombinant DNA technology (gene insertion).
• CRISPR-Cas9 for precise gene editing.

DNA Analysis Methods

• PCR: Used to amplify DNA segments.
• Gel electrophoresis: Separates DNA fragments by size.
• DNA sequencing: Determines the exact base order.

Applications

• Medicine (e.g., producing insulin), agriculture (e.g., Bt cotton), and forensics (DNA profiling).

Module 7: Infectious Disease

Pathogens

• Types: Virus, bacteria, fungi, protists, and prions.
• Transmission: Direct contact, indirect contact, airborne, vector-borne, or waterborne.

Disease Processes

• The sequence: Entry → reproduction → tissue damage → symptoms.
• Virulence factors include toxins, adhesion molecules, and mechanisms for evading host defenses.

Immune Response

1. Non-specific (Innate): Skin, mucous membranes, inflammation, and phagocytosis.
2. Specific (Adaptive):
   • B cells: Produce antibodies.
   • T cells: Destroy infected cells.
   • Memory cells: Provide long-term immunity.

Prevention & Control

• Vaccination, quarantine procedures, strict hygiene, and public health campaigns.

Module 8: Non-Infectious Disease and Disorders

Causes of Non-Infectious Disease

• Genetic: Inherited mutations (e.g., cystic fibrosis).
• Environmental: Exposure to radiation or carcinogens.
• Nutritional: Deficiency or excess of essential nutrients.
• Lifestyle: Smoking, poor diet, inactivity.

Epidemiology

• Studies the patterns, causes, and distribution of diseases.
• Helps identify risk factors and guides prevention strategies.

Prevention Strategies

• Education, regular screening, lifestyle modification, and targeted vaccination where applicable.

Management Technologies

• Insulin pumps (for diabetes).
• Cochlear implants (for hearing loss).
• Gene therapy.
• Artificial organs and prosthetics.

Homeostasis Failure

• Disruption in feedback mechanisms leads to disease (e.g., Type 1 diabetes resulting from insulin deficiency).

Bonus: Formula & Concept Quick Reference